BOSTON — The game within the game tonight at TD Banknorth Garden hit its pinnacle in the third period. After David Krejci used some slight of hand — and a little luck — to give the Boston Bruins the lead for good, Marc Savard extended the lead with a pretty move of his own just four minutes later.

Watching this Bruins team, it’s always hard to tell which of their top lines is supposed to be the first — and no place was that more evident than in the club’s 6-4 win over Ottawa.

Hockey players and coaches cringe at the thought of numbering lines — insisting that everyone’s equal and an NHL line is an NHL line. But we all know that’s just their team unity talking and their has to be a hierarchy. There has to be a line the coach goes to when he needs a goal, one he goes to in order to protect a lead, one he counts on to change the game with some physical play.

Boston Bruins head coach Claude Julien has been lucky enough to sometimes have three lines consistenly scoring. But injuries to Patrice Bergeron, Marco Sturm, and now Milan Lucic, have sort of thinned the Bruins’ herd up front and forced the team into having more traditional checking and scoring lines. Determining which line is the top one — among the Krejci and Savard lines — is where things get sticky.

Although the Krejci line seemed to have the upper hand against Ottawa — Krejci and Michael Ryder tallied two points apiece and Blake Wheeler added an assist — Savard, Phil Kessel and their left winger of the night Chuck Kobasew (a part sometimes played by Lucic or P.J. Axelsson) held their own with six points among them.

There’s definitely a friendly rivalry going on — one that can only help drive the Bruins where they want to go.

“(Savard) jabs us a little bit about the plus/minus, and he’s a tough guy to catch,” Wheeler said after the game. “But it’s fun because I think the great thing about us is nobody’s satisfied ever. You want to keep going and get more and you’ve got to have that hunger. I think we’ve done a good job of kind of putting the nail in the coffin.”

For the record, Savard is now plus-28 on the year, so Wheeler (plus-25), Krejci (plus-23) and Ryder (plus-19) are still looking up at the All-Star center in the team rankings. But you factor in the Krejci line’s 12 game-winning goals (not all scored as a trio, but substantial nonetheless), and the edge probably goes to the threesome centered by the Czech native.

For style points, Krejci prevailed as well against the Sens. With the scored tied at 3, Krejci went to the net and flipped a shot on goal that deflected off Ottawa goaltender Martin Gerber’s skate. The puck went behind Gerber’s back and out the other side to Krejci for the flip-in.

“I guess it was lucky. At first I thought I hit a post or I didn’t see the puck. And then I saw it in front of me. So I guess we can talk about luck a little bit there,” the pivot said.

Savard tried to outclass Krejci with a move to the slot that ended with a wrist shot finding space between Gerber and the left post for a 5-3 lead with 5:31 left. But for jump-out-of-your-seat excitment, the Krejci goal had a slight edge.

And that’s the same sized edge the Krejci line has right now in the battle for No. 1. This is a debate that’s sure to rage all season long, and get more interesting once Lucic and maybe Sturm return from injury, or Kobasew settles in as the permanent left side.

The best part is, there’s no BCS system here, there’s no computers determining anything and there are no polls. The fight to be the Bruins’ top line will be determined on the ice. The best line will win and the Bruins as a franchise will reap the rewards.